Crash when MIDI events are received after an MIKMIDIConnectionManager has been created then deallocated.

[armadsen]

Reported in Issue #214. To reproduce, create a new, empty project with the following:

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
	_ = MIKMIDIConnectionManager(name: "test")
	return true
}

Run the app with a MIDI device already connected. After the app launches, press a button on the MIDI device and watch the app crash here:

- (BOOL)internalConnectToDevice:(MIKMIDIDevice *)device error:(NSError **)error
{
	if ([self isConnectedToDevice:device]) return YES;
	error = error ?: &(NSError *__autoreleasing){ nil };
	
	__weak typeof(self) weakSelf = self;
	id token = [self.deviceManager connectDevice:device error:error eventHandler:^(MIKMIDISourceEndpoint *endpoint, NSArray *commands) {
		[weakSelf recordPendingNoteOnCommands:commands fromDevice:device];
		[weakSelf removePendingNoteOnCommandsTerminatedByNoteOffCommands:commands fromDevice:device];
		
		weakSelf.eventHandler(endpoint, commands); // *** CRASH ***
	}];

<snip>

}